The SIP is a VoIP signaling protocol proposed by the Internet Engineering Task Force (IETF). The SIP is used to initiate a session, control establishment and termination of a multimedia session with a plurality of participants, and dynamically adjust and modify attributes of the session, such as a bandwidth requirement of the session, the type of transmitted media (voice, video, text, etc.), encoding and decoding format of the media, the support for multicast and unicast. In an IP multimedia Subsystem (IMS), the SIP protocol is adopted as a signaling control protocol for an IP multimedia session.
Standardization organizations, such as the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), have proposed IMS architectures, for the purpose of implementing various multimedia applications through a standardized open framework in a mobile network to provide more choices and colorful experience for a User Equipment.
In the 3GPP Release 5 (R5) phase, the introduced IMS is deployed over a packet domain network, and consists of such function entities as a Call Session Control Function (CSCF) module, a Media Gateway Control Function (MGCF) module, a Multimedia Resource Function (MRF) module and a Home Subscriber Server (HSS). The CSCF may be further divided into three logical entities of a Serving CSCF (S-CSCF), a Proxy CSCF (P-CSCF) and an Interrogating CSCF (I-CSCF). The S-CSCF is a service switching center of the IMS for performing session control, maintaining a session status, managing information of the User Equipment and generating charging information; the P-CSCF is an access point for a User Equipment to access the IMS, and is adapted for accomplishing registration of the User Equipment, controlling Quality of Service (QoS) and implementing security management; and the I-CSCF is adapted for intercommunicating with the IMS domains, managing allocation of S-CSCF, concealing the topology structure and configuration of the network from the outside, and generating charging data. The MGCF is adapted for controlling a gateway and intercommunicating with IMS networks. The MRF is adapted for providing media resources such as a ring tone, a codec and a multimedia conference bridge. The HSS is a subscriber database for storing subscription information, configuration information of IMS subscribers, etc.
During a negotiation on the establishment of a multimedia session based upon the SIP protocol, there is a demand for carrying multimedia information in a session negotiation message and providing other multimedia information in addition to signaling during the session negotiation. The multimedia information carried in the session negotiation message can be added by the initiator of the session, or can be obtained from multimedia resources of a network entity.
SIP protocol messages include, for example, a SIP INVITE message, a SIP REFER message, a SIP MESSAGE message, a SIP INFO message, a SIP OPTION message, a SIP 2XX OK message, and a SIP 1XX message, etc.
The SIP protocol message supports embedding various types of message contents into the message, and the embedded message contents may be a text, a picture, a video clip, a sound file and/or an executable program. Some message contents related to the session, such as a piece of text or a reference to the message contents, may be embedded into the message header.
For example, in the prior art, a ring tone file is stored in a User Equipment in the form of a sound file, and if the receiving User Equipment receives and accepts an INVITE message, the receiving User Equipment plays the ring tone file.
In a first prior art, a ring tone is stored in a User Equipment, and no ring tone file or play program is stored in an INVITE message and a SIP 180 (Ring) message. Instead, a ring tone to be played is selected by the User Equipment in accordance with the setting of a subscriber. No network entity in a SIP network provides the SIP User Equipment with a ring tone file. Instead, the ring tone file is stored in the User Equipment.
Various individualized ring tones provided in the first prior art are fully dependent upon ring tone files stored in the User Equipment. Therefore, neither the individualized ring tone provided for the present session by the SIP network nor operation by the operator and the network on multimedia information of the session may be embodied.
In a second prior art, as specified in the IMS specification, an MRF may act as a multimedia resource and play a ring tone for a receiving User Equipment during a session negotiation. In FIG. 1, a schematic diagram of a flow in which an MRF plays a ring tone for a receiving User Equipment is shown. As specified in the IMS specification, a connection is established between the MRF and the receiving User Equipment, so that the MRF may play a multimedia ring tone for the receiving User Equipment.
The solution of the second prior art causes many processes to be added during the session negotiation, and multimedia information provided by the MRF for the receiving User Equipment includes only a ring tone, which may be tedious because no other multimedia content or application program can be provided. From the view of system performance optimization, the session negotiation of this method is rather time-consuming, but few functions can be obtained. Furthermore, the message content of a SIP message are defined in the prior art, and an application server for message contents of the SIP message generated by a SIP message initiator may not process new media contents, which is also a drawback.
For the purpose of transmitting only media contents, some network resources may be still consumed due to the size of the media contents. In some cases, however, if a client or a server stores the media contents, during the actual transmission, it is also possible that no actual media resource but just a reference recognized by both parties is transferred, and a receiver may retrieve the media contents in accordance with the reference. And thereby the utilization rate of network resources is improved. The media contents and the reference to the media contents carried in a SIP message are referred to a media component. Furthermore, in a method for transferring media contents or a reference to the media contents, the addition of abundant media contents or a reference may be managed in accordance with an operator policy or subscriber subscription or the setting in the subscription.